Surface plasmon is a phenomenon that has been employed in the design of, for example, sensors, nonvolatile memory, and photonic devices. A surface plasmon is a surface charge density wave at a conducting surface excited by, for example, monochromatic light, X-ray radiation, or modulated frequency pulse. The propagation of a charge wave may come into resonance with a photon of energy from an excitation source, leading to a so-called surface plasmon resonance (SPR). This resonance is sensitive to the miniscule concentration of substances on top of the surface, or can be utilized in spontaneous charge/discharge/photon emission in nanostructured layers, paving the way for design of photonic and memory devices.
Phenomena involving plasmons have been the subject of study in recent years in seeking to overcome some limitations of conventional signal transfer in electronics (W. L. Barnes, Devaux, E., Ebbesen, T. W., Nature, 424, 825 (2003), W. L. Barnes, Murray, W. A., Dintinger, J., Devaux, E., Ebbesen, T. W., Physical Review Letters, 92, 107401 (2004)) and lowering the threshold of detection in biosensing. In general terms, a plasmon is a localized charge density wave or electronic plasma, oscillating near the surface or in the bulk of a material (H. Raether, in Physics of Thin Films, Volume 9, G. F. Hass, M., Hoffman, R. Editor, pp. 145-261, Academic Press, New York (1977), C. Nylander, Liedberg, B., Lind, T., Sensors and Actuators, 3, 79 (1982/1983), P. Steiner, Höchst, H., Hüfner, S., Physical Review A, 61A, 410 (1977)). The ability of this wave to come into resonance with a quantum of energy from an excitation source is instrumental for the design of plasmonic devices with a potential to excel in a variety of applications.
Devices based on surface plasmon resonance (SPR) have already found use in, for example, biochemistry and the pharmaceutical industry (C. Nylander, Liedberg, B., Lind, T., Sensors and Actuators, 3, 79 (1982/1983), J. Homola, Analytical and Bioanalytical Chemistry, 377, 528 (2003)), where SPR has been used to follow biochemical reactions and/or molecule adsorption on surfaces. In these applications, the plasmon is generated at the interface of dielectric and conducting layers. Through proper optical alignment of a Kretschmann's prism, the parallel component of incident light matches the dispersion of surface plasmons at the interface, thus giving a rise to the SPR. The Kretschmann's arrangement is very strict in terms of incident angle, laminarity of the layers, film thickness and, therefore, requires a precise manufacturing.
A variety of plasmonic devices have been developed by utilizing the ability of nanoparticles to absorb the light (W. L. Barnes, Devaux, E., Ebbesen, T. W., Nature, 424, 825 (2003), W. L. Barnes, Murray, W. A., Dintinger, J., Devaux, E., Ebbesen, T. W., Physical Review Letters, 92, 107401 (2004), S. A. Maier, Kik, P. G., Atwater, H. A., Meltzer, S., Hard, E., Koel, B. E., Requicha, A. G., Nature Materials, 2, 229 (2003)). These include waveguides, filters and polarizers (S. A. Maier, Kik, P. G., Atwater, H. A., Meltzer, S., Harel, E., Koel, B. E., Requicha, A. G., Nature Materials, 2, 229 (2003)), nanoscopic light sources (H. J. Lezec, Degiron, A., Devaux, E., Linke, R. A., Martin-Moreno, L., Garcia-Vidal, F. J., Ebbesen, T. W., Science, 297, 820 (2002)) and tunable plasmonic devices (Y. Leroux, Eang. E., Fave, C., Trippe, G., Lacroix, J. C., Electrochemistry Communications, 9, 1258 (2007), Y. Leroux, Lacroix, J. C., Chane-Ching, K., Fave, C., Felidj, N., Levi, G., Aubard, J., Krenn, J. R., Hohenau, A., Journal of the American Chemical Society, 127, 16022 (2005)). The absorption of light by nanoparticles varies with size and material and in turn provides a means to adjust the wavelength of absorbed light. The absorption of light in the visible or near-infrared region by nanoparticles has been explained by the presence of localized surface plasmons (LSP) (Y. Leroux, Lacroix, J. C., Fave, C., Trippe, G., Felidj, N., Aubard, J., Hohenau, A., Krenn, J., Journal of the American Chemical Society, 2, 728 (2008)), which depends on size and shape of nanoparticles. By coupling these systems with a surrounding medium that can be modulated, it may be possible to create switchable or tunable devices based on this phenomenon.